The words "human" and "man" are etymologically unrelated. It's just a coincidence they both have m-a-n in them.
and for man:
"Old English man(n), (plural) menn (noun), mannian (verb), of Germanic origin; related to Dutch man, German Mann, and Sanskrit manu ‘mankind’."
Interestingly enough, Manu was "the progenitor of mankind" and in Persian (which shares roots with Sanscrit) after Islam the equivalent "progenitor" Adam [aa-dam] is also commonly used to intend 'mankind'.